The work deals with the description of and genetic control of development in Polysphondylium pallidum, a cellular slime mold which exhibits integrated multicellular development. The experiments are of three sorts: 1. A detailed description of changes in labeling of specific proteins during the aggregative phase of development will be made. This will utilize autoradiography of two-dimensional polyacrylamide gels. 2. The hypothesis that the order of the observed protein labeling changes is controlled by a chain reaction of causes (a "causal sequence") will be tested. Experiments here will utilize temperature-sensitive developmental mutants, double mutant haploid strains derived from two different developmental mutants, and chemical agents which specifically affect development but not growth. 3. The regulation of particular labeling changes will be studied by genetic investigation of groups of developmental mutants which appear to block a single step of the causal sequences. Parasexual techniques will be used to test complementation between pairs of strains within such a group, and to assign them to linkage groups. The map positions of mutations on the same linkage group will be determined by means of the alternate meiotic sexual cycle.